1. Field of the Invention
The present invention relates to a system (i.e. method and apparatus) for detecting a near empty state of a toner bottle used for replenishing a developing unit with a toner in an image forming apparatus using a toner.
2. Related Background Art
In an ordinary apparatus for image formation using a toner, such as an electrophotographic apparatus, it is a general practice to dispose a toner bottle or cartridge (hereinafter, representatively called “bottle”) for replenishing a developing unit with a toner, as desired, depending on the toner quantity in the developing unit. In this instance, it is desired to monitor the toner bottle so that a fresh toner can be incessantly replenished in response to a demand from the developing unit and, on reaching a near empty state close to an empty state, a spare toner bottle is provided so as to allow an immediate exchange of the toner bottle on reaching the empty state and obviate the interruption of a necessary image forming operation. For the detection of such a near empty state of toner bottle, there has been adopted a method of detecting a remaining quantity of toner in and a near empty state of a toner bottle based on a change in rotation speed of the toner bottle required for the replenishment which speed varies depending on the toner remaining quantity in the bottle (Japanese Laid-Open Application No. 2001-35934 (JP-A 2001-35934, U.S. Pat. No. 6,289,182)), or a method of detecting a near empty state when a number of replenishment times by rotation of a toner replenishing roller for supplying a toner from a toner bottle to a developing unit reaches a prescribed number for judgment of toner empty under a correction with a certain correction factor (JP-A10-207212, U.S. Pat. No. 5,286,134).
However, the former method of judging a near empty state based on a change in rotation speed of a toner bottle involves a problem that a large fluctuation occurs in motor torque or load of the rotation mechanism. Further, the latter method based on the replenishment times by the replenishing roller involves a problem that the corrective judgment with a correction factor is complicated so that a good accuracy of judgment of the near empty state cannot be attained.